My son is on business in china.. He has a 3 month business M type with a 30 day stay..

Feroza, he can extend his business M type, but the extended time cannot exceed 30 days. First, prepare the relevant materials: his passport, the application form, a passport-style photo, valid registration form of temporary residence, and an invitation letter from his business partner, as well as other documents the consular officers consider necessary.
Next, go to the exit and entry administration of the local PSB to apply the extension.